Full form of PHBV biodegradable polymer :

Question

UnlockIAS · Accepted Answer

Correct — C, Poly (3 - Hydroxy butyrate-co-3 hydroxy valerate). The acronym decodes letter by letter: P for poly, HB for 3-hydroxybutyrate, V for 3-hydroxyvalerate. PHBV belongs to the polyhydroxyalkanoates or PHAs — a family of polyesters that are not manufactured from petrochemicals at all but produced inside living cells, by bacterial fermentation of sugars or lipids, and stored as intracellular granules that serve the microbe as both an energy source and a carbon store. More than 150 different monomers can be combined within the family, giving materials of very different character with melting points from 40 to 180 °C, and the polymer harvest from those granules can reach 80% of the organism's dry weight. Two details of option (c) prove it is the real chemical name rather than a plausible string. First, the locant '3-' in front of each monomer states exactly where the hydroxyl group sits — on the third carbon of a four-carbon butanoate unit and of a five-carbon pentanoate (valerate) unit. Second, the infix 'co' is IUPAC copolymer notation: poly(A-co-B) means a single chain built from both repeating units, not a blend of two separate polymers. That copolymer structure is the entire reason PHBV exists commercially. Pure poly-3-hydroxybutyrate, PHB, was the first PHA discovered and it is a disappointing plastic — highly crystalline, stiff and brittle, melting at 175 °C with a glass transition of only 2 °C and a tensile strength near 40 MPa, close to polypropylene's, but far too brittle to process comfortably. Threading hydroxyvalerate units into the chain disrupts the crystal packing, and crystallinity across the PHA family ranges from a few per cent to about 70%: PHBV is accordingly less stiff and tougher than PHB, and its processability, impact strength and flexibility all improve as the valerate fraction rises. That toughening is why PHBV, and not PHB, is used as a packaging material — and why the examiner chose it as the model biodegradable polymer.

Why the other options are wrong — (a) Vanillin — spelt 'vaniline' here — is a genuine compound, 4-hydroxy-3-methoxybenzaldehyde, the molecule that gives vanilla its flavour, and its aromatic ring does appear in some experimental bio-polymers. But it is an aldehyde, not a hydroxy acid, so it cannot form the ester linkages that define a polyhydroxyalkanoate. 'Butyl' is also wrong in kind: an alkyl substituent, not the butyrate ester unit the B stands for.  (b) Two independent errors, either of which is fatal. Butane is a saturated alkane with no functional group at all, so nothing about it can polymerise into a polyester — the monomer is butyrate, the butanoate anion. And veratric acid, 3,4-dimethoxybenzoic acid, is an aromatic plant acid that has nothing to do with the aliphatic five-carbon valerate the V denotes.  (d) The near-miss, and the option that catches a candidate with partial knowledge. Its first half is genuinely right — 3-hydroxybutyric acid is the HB monomer. It then substitutes veratric acid for valeric acid, and the V in PHBV is valerate (pentanoate, five carbons), not veratric. It also omits the 'co' infix, so even read charitably the name describes two acids rather than one copolymer chain.

Concept: Most plastics in use are synthetic polymers made from petrochemicals, and they resist biodegradation because no common enzyme recognises their carbon backbones. Polyhydroxyalkanoates take the opposite route: they are made by micro-organisms, they are true polyesters, and soil and sludge bacteria of the genera Bacillus, Pseudomonas and Streptomyces can eat them back down. Production is a fermentation, not a cracking plant. A culture such as Cupriavidus necator is grown to high density on glucose, sucrose, vegetable oil or biodiesel glycerine, and is then deliberately starved of a nutrient — nitrogen, phosphorus, a trace element or oxygen — while carbon is kept in excess. The stressed cells respond by laying down PHA granules, which are recovered by rupturing the cells. Keep two distinctions straight, because examiners exploit both. Bio-BASED is not the same as biodegradable: bio-PET made from sugarcane ethanol is renewable in origin yet persists exactly like fossil PET, while PBAT is petroleum-derived and still compostable. And biodegradable is not the same as compostable, which is a certified performance claim about breaking down under defined industrial composting conditions in a defined time. PHAs happen to satisfy all three descriptions at once — bio-based, biodegradable and compostable — which is why they are the standard classroom example, and PHBV is the standard example within the family.

State PCS 2025 Q138 — Science & Technology PYQ with Answer

State PCS 2025 Q138 — Science & Technology PYQ with Answer